This is a very interesting discussion going on there with several people who have training in the field of dam/rain dynamics making interesting remarks and I decided to pull up several of these to illustrate what is going on according to people who know their stuff better than I:

Chris4692 February 20, 2017 at 8:24 am
Note that there is seepage in this joint, but not those joints downhill. The spillway slab in this steeper portion is constructed on a granular fill. That granular fill is drained by a system of drains. That there is seepage indicates that the drainage is either overwhelmed from the wet conditions and the drainage from above or has plugged. The granular fill continues to the bottom of the spillway. Even though the drainage system is overwhelmed in this location, water below the slab should drain through the granular material, preventing it from becoming saturated at this point. It is blocked by something, perhaps a rock outcropping up to the bottom of the slab that prevents the water from moving.

This is not a failure of the joint, it is a failure of drainage. Joint sealing methods from the 1960’s would not be able to withstand more than a slight pressure from below.

Views showing the spillway working at 100,000 cfs show the water moving around the lower part of the spillway, deflected by something. Likely the hypothesized outcropping. Granular material under the slab would have been blasted away by the water long ago if not protected by a solid rock outcrop or something similarly solid.

The significance is that with hydraulic pressure from drainage higher on the hill connected to saturated conditions below the slab there would have been a significant upward force (buoyancy) lifting the slab. It would only take a few feet of water pressure from below to dislodge the slab and cascade into the failure seen.

Though there are other possible modes of failure that must be examined, and each has to include a consideration of “why now and not before?” This seems to me to be the most likely.

ristvan February 19, 2017 at 2:25 pm
As calculated both earlier here and elsewhere, 10 inches in the watershed is dicy. 12 is a lot worse. They have the lake down near 850, but have not yet cleared the debris bar in order to be able to use the power station 14000CFS discharge. And doubtful the damaged main spilway will be run above 100000CFS for fear of back erosion. That has to hold. Lot will depend how much of this precip falls as snow. If a lot falls as rain on snow, the situation becomes dire in a hurry.

The main spillway is separated from the dam by a mountain side that is at least partly fairly solid bedrock. You can see this at two points: at the top, where the (viewed from below) right side upper spillway was cut by drilling and blasting of black rock, and at the bottom where the break flows right of rock to right of spillway that has not crumbled (and is also black,like at the top. That the water flows white says no more erosion scour is happening at the bottom. The spillway exit is into the diversion pool at the bottom of the actual earthen dam, which is why the debris bar is posing a problem for the powerhouse located at that level but inside the mountain. Cut a channel through the debris bar, open the powerhouse penstock, and the water will erode the remaining debris bar some. (obviously not the big concrete chunks or boulders, but the mid and sand soil.)

E.M.Smith February 19, 2017 at 11:03 pm
I put a comment above describing that the spillways are built on a natural ridge of rock with a 1000 foot tall or so mountain (really big hill to folks not from Texas or Kansas) between the spillways and the dam.

There is a fairly long chunk of river back to the powerhouse, that is built into the opposite side of the dam / hillside. It has water too high at the moment so if they opened it up, the powerhouse would flood. Once debris is cleared, the pool will drop, and it can be opened, BUT:

They can’t run the generators without power lines active and attached to provide sync and a place for the power to go, and those power lines go over the spillways and one of the towers is at risk of erosion…

It is only about 13,000 CFS of water, though, so not a huge add.

nc February 20, 2017 at 1:19 am
E. M. Smith, the generators can be run without generating power but water flow will greatly reduced. Think of low fuel flow with an idling engine.

If the power line fails some water can still be discharged through the powerhouse but at a reduced rate. The debris in the river will most likely have to be cleared first.

taxed February 19, 2017 at 2:30 pm

Between next Friday and Saturday its looking like things could get very bad indeed,as there will be a “ice age pattern” forming in the NE Pacific.
High pressure will form in the NE Pacific which will be driving warm air up into the Arctic over Alaska, but pushing cold air from northern Canada down across NW USA and over the Pacific to the west of the USA. With this cold air moving from the NE over the Pacific meeting up with warm moist moving westwards. Will set up a very powerful slow moving storm which will track over the California area.

The regular spillway has very little water running down the chute, 90% of it exploded sideways, eating out the hillside next to the spillway. It has excavated quite a deep run there, to that side. Amazing to see.

9 responses to “3D Explorer Of Oroville Dam…Cool Fun”

That last video is great. If I were a civil engineer and given five days to patch the emergency spillway, that's what I would have done. Rocks, concrete, more rocks, more concrete. All along the natural gullies that were ripped out by the recent flood.

Whether it holds up, of course, is another matter. Depends on how much rain comes down the next few days, I expect.

Interesting to see what has happened to the main spillway, too. It's making its own path through the mountain. Which is a tectonic mishmash of pudding-stone and hard bedrock. Thanks for finding that video.

Not much news that hasn’t already been discussed. Nice picture of the end of the main spillway — all that water should be coming straight out toward the camera, but as you can see, it’s going off to the side. 60,000 cfs. No progress on clearing the outlet for the power plant.

Still putting down rocks and concrete to fill up the gullies. And hoping they don’t have to let any water go through it…